1. Field of the Invention
The invention relates to a hydraulically driven working vehicle, especially, a four-wheel drive working vehicle, equipped with front wheels and rear wheels driven by respective hydraulic motors, and relates to a hydraulic transaxle including the hydraulic motor applicable to the vehicle. An example of the hydraulically driven working vehicle according to the invention is a lawn tractor equipped at the middle body portion thereof with a mower unit. The transaxle according to the invention can supply fluid to hydraulic equipments equipped on the hydraulically driven vehicle, e.g., a hydraulic power steering system, in addition to the hydraulic motor for driving an axle.
2. Related Art
Conventionally, there are well-known hydraulic four-wheel drive working vehicles, each of which is equipped with front and rear hydraulic motors for driving front wheels and rear wheels. A hydraulic four-wheel drive working vehicle, as disclosed in International Publication No. 2004/062956, is provided with a rear transaxle including a hydraulic motor for driving left and right rear wheels, and with a front transaxle including a pair of left and right hydraulic motors for driving respective left and fight front steerable wheels. This type of hydraulic four-wheel drive working vehicle is equipped at a middle portion thereof between the front and rear transaxles with a traveling power transmission system for transmitting power from a prime mover to the rear transaxle, and with a working power transmission system for transmitting power from the prime mover to a working device. In this situation, the front and rear transaxles are fluidly connected to each other via pipes for driving the front and rear wheels (axles), and the axle-driving pipes have to be disposed at the middle portion without interfering with the traveling power transmission system and the working power transmission system.
To miniaturize the hydraulic four-wheel drive working vehicle, the pipes are requested to be disposed within a space inside a vehicle body frame. However, the space is mainly occupied by the traveling power transmission system and the working power transmission system. Further, the vehicle may be equipped under the fore-and-aft middle portion of the vehicle body frame with a working device, such as a mower unit.
The axle-driving pipes have to be disposed in the space between the front and rear transaxles without interfering with the traveling power transmission system and the working power transmission system, and the working device at need. Further, to facilitate assembly works, the pipes are desirably disposed so as to require no device to be detached during the piping work of the pipes, and to require no pipe to be detached during attachment of other devices. On the other hand, in order to reduce internal pressure resistance in the pipes, the pipes are requested to have reduction of bent portions therein and to have rigid pipe portions as long as possible. Especially, the pipes have to be prevented at portions thereof adjacent to a center pivot of the front transaxle with being excessively twisted or bent, and prevented at portions thereof connected to ports from having an oil leak or being damaged.
If the hydraulic four-wheel drive vehicle includes a hydraulic power steering system, hydraulic fluid pipes for the power steering system must be disposed so as to solve the same problems as the axle-driving pipes.
Further, if the vehicle is provided with a reservoir tank for supplying fluid to the hydraulic motors in the front and rear transaxles, it is requested that the reservoir tank is disposed so as to be prevented from interfering with the traveling power transmission system and the working power transmission system, to have easy oiling and maintenance, and to effectively supply fluid into the housings of the front and rear transaxles. Especially, when the front transaxle housing is swingably supported onto the vehicle body frame via a center pivot, the reservoir tank is requested to prevent fluid therein from being contaminated with air by tilt of the fluid level surface according to the swing of the front transaxle housing, and to prevent hydraulic pressure fluid pipes between the reservoir tank and the transaxles from being twisted by the swing of the front transaxle housing.